Fluid actuated servomotor control system



my 9 3952 G. T. RANDQL FLUID ACTUATED sERvoMoToR CONTROL SYSTEM Filed NOV. 17, 1.947 2 SHEETS-SHEET 2 INVENTOR.- Glenn 7'. Randal,

ATTOR NE YS.

- which: y

Patented July 8, 1952 UNITED STATES 'arcaica rem f .orFlCE Iranno ACTUATED sERvoM-o'rort ooN'riaoL l SYSTEM Y 4Glenn T, Bandol, Fort Lauderdale, Fla. application November Y17, 1947, serial No.78a498 jiiciaimsg (o1. 1er-4c) of a piston-type servomotor in a positionto` which it has been moved by differential iiuid pressure.

Another object is to so embody electro-rnagkv netic holding means in a servomotor that the energizing coil is incorporated directly in the movable element of the motor.

Yet another object is to provide improved con-v trol means for a double-acting servomotorwhich will cause the piston element thereof to bernoved by diierential fluid pressure to either extreme position and held in such positions by electromagnetic means. Y n n Still a further object isto providev improved means for so controlling the. movable v'element of a double-acting piston-type fservomctor that said element can, under certain operativeconditions,

be moved to either end of its stroke :by differentialv fluid pressure and magnetically heldat said ends;

or under other operative conditions causedto asvsume an'intermediate position Without the action of differential fluid pressure. p `A more specific object is to so embody electromagnetic holding means inauid pressure op@` erated servomotor for the-movable element thereof that a compact and low cost motorof this type can be produced. Y

Still another object is to produce an improved speed responsively controlled double acting servomotor that will cause the movable yelement thereof to assume positions at either end of its strokeor an intermediate position, dependingon the speed of a member to which said device is responsive. s y

Other objects of the invention will become; apparent from the following description takenin connection with the accompanying drawings in Figure 1 is a View of a servornotorcontrol system shown, by way of example, as embodying the invention, the servomotor being Ashown' insee-Y tion, parts of the control valves being broken away and the system conditioned so that. the piston of the servo-motor is in its central position,

to provide.

is to provide iinprovedelectro-l port I9.

non-energized portions of the electrical lcircuit being shown in dotted outline; Y

Figures 2, 3V and 4 are various cross sectional views of the servomotor showing details thereof,v

' piston of` the servomotor is moved to the leftnend of its strol e non-energized portions of the electrical circuit being shown in dotted outline; and

Figure 7 is another viewsimilar to Figure l,

but showing the condition of the control system when the piston of the servomotor is moved to the right end of its stroke, non-energized portions of the electrical circuit being shown in dotted outline. l l

Referring tothe drawings in detail, the fluid servomotor control system shown 'as embodying the invention comprises as its essential elements a servo-motn'v M,Ya source of fluid pressure different from atmosphere shown as a tank T, ftwo solenoid-operated control valves Fand R of identical construction, a speed-responsive device S anda servomotor actuated element shown as a lever L,` and a source of electricity for the various electrical circuits shown as a battery B.

The uid servomotor M is of the double-acting piston-type and comprises a cylinder I0 having an integral right end wall l I and a removable left end wall i2 and secured to the inner side thereof as by riveting is a Asaucer-shaped spring retainer I3. Within the cylinder is a reciprocal piston generally indicated by the letter l? which has connecte'd thereto a piston rod i4 extending through a packing inthe left end wall vl2 of the motor. The -outer end of this piston'rod is pivotally connected to the lever L which by way of example, is to be 'actuated by the piston. The lever L has one arm "i5, to. the free end of which is pivotally connected'the piston rod i4, and a second arm I6 to which is operably connected a rod i'l leading to any' `particular mechanism which it is desired to actuate. 'Ihe arms l5 annd IG, forming the lever L! are pinned to a commonpivot shaft I8 which is arranged to be journaled in any suitablesupservom'otor is arranged to be'pivotally mounted on any suitable supportV and to accomplish this the right Wall carries a clevis 2B pivotallyxconnected by aj pin 2l with a bracket 22H secured as but show-1 The right end ofy the cylinder `roi" the l by bolts to any convenient support structure 23. The particular servomotor shown, is arranged to be actuated by differential fluid pressure created from a source of sub-atmospheric pressure and, as already indicated, this is shown as a tank T. The sub-atmospheric pressure in the tank T, of course, will be established from some original source such as the intake-manifold of a combustion engine or a suction pump, neither of which is illustrated. Leading from the tank T are branch conduits 24 and 25, branch conduit 24 being connected through the valve F to a conduit 26 leading to the left end of the cylinder l0 of the servomotor. Branch conduit is connected.

through the valve R to a conduit 21 leading to the right end of the cylinder of the servomotor.

Since the valves F and R are identical in construction, details of each are referred to by similar reference characters. Each valve comprises a casing 28 having an inlet chamber 29 which is to bev connected to the tank T and an outlet chamber 30 which is connected to the servomotor. Between these two chambers is a partition 3l having a port 32 with which is associated a valve element 33; This valve element is positioned in chamber 30 and is mounted on the reduced end of the armature'34 of the solenoid 35. When thesolenoid is de-energized a spring 35 is effective to act on the armature 34 to normally move the valve element 33 upwardly and close the port 32 so that communicationbetween the tankand the servomotor is cut off. The chamber 30 is also arranged to beclosedoff from the solenoid and atmosphere,v

when theport 30 is opened by thel valve element.

This isaccomplished by a partition 31 having Va port 33 through which the reduced portion of theV armature 34 extends. This port 38 is arranged to be open whenever the Valve element 3-3 closes the port 32.4 When the solenoid is energizedto move the armature downwardly and overbelow the partition 31 and above the solenoid arranged tol be in constant communication with the atmosphere through an air port 39. The purpose of this air port is to insure that whenever the valve element 33* is closing off port 32, the chamber-39 andV the connected end of the motor will be in free communication with the atmosphere.

With the valves F and R constructed as shown and described, it will be seen that the opposite ends o f the servomotor can be connected either to the tankv T or to atmosphere. If the solenoidsr of both the valves F and R are de-energized, then both ends of the servomotor will be disconnected from the tank T and connected to atmosphere. If the solenoid of the valve F only should be energizedl then the tank'T willbe connectedV to the left end of Vthe servomotor and consequently a dierential uid pressure will be so effective upon the piston as to move the piston to the leftV end of thev servomotor. If the solenoid of the valve R' only should be energized, then the tank T will bevconnected to the right'end of the'servomotor and differential fluid pressure will be soA effective upon the piston P that it will be caused. to move to the right end of the servomotor.

The valves F and R are arranged to be selectively controlled by a speed-responsive devicealready referred to .by the letter S. This device has a 4 shaft 40 which is rotated by a driving shaft 4| through gears 42 and 43. The driving shaft may be responsive to any rotating member such as, for example, the wheels of a motor vehicle if the control system is to be used on such. Pivotally mounted on the shaft 4U are two centrifuge members 44 and 45, the upper ends of which are connected by links 46 and 41 to a sleeve 48 carrying a conductor ring 49. A spring 50 normally biases the sleeve and conductor ring to an upper position which is the substantially normal rest position for the centrifuge members. The conductor ring. 49 is a movable element of a switch which is to be controlled by the speed-responsive device S. The conductor ring is arranged to be in constant engagement with a fixed contact member 5I which is grounded Iby Way of a conductor 52, said conductor also being employed to energize a coil of an electro-magnet incorporated in the piston of the servomotor, as will become apparent later. The conductor ring is selectively engageable with fixed contact elements 53` and 54under'the action of the speed-responsive device. The contact element 53 is connected by a conductor 55Y to. one terminalof the solenoid 35 ofthe valve. F.

The other terminal of this solenoid is connectedV by a conductor 56 to one terminal of theY battery B, the other terminal of said battery being grounded by a conductor 51 so as to completeV a. circuit. The other contact element 54M is con-v nected by a conductor 58j to oner terminal of the solenoidl 35 of the valveR.y The other terminal of vthis solenoid is connected byV a conductor 59' to the same terminal of the battery B, ras is conductor 56. v

With the aforementioned connections for thesolenoids of the two Valves F and R, it will bev seen that if the conductor ring 49-controlled by the speed-responsive device is in engagement with thecontact 53, a circuit will be established, energizing the solenoid 35- of the'valve F. If the conductor ringv 49 is moved to a position wherein it engages the contact 54', then a circuit will be established. which will energize the solenoid of the valve R. The contacts 53r and 54 are so spaced apart and arranged with respectto the ring contact 49 that when the speed-responsive device is' substantially at rest, the ring contact will be. above Athe contact 53I as shownin Figure l, and neither of the. circuits forthesolenoids of the valves F and Ry will be energized. However, if the shaft 40 should beso rotatediin response to the speed of a rotating member'. that the centrifuge members will move sleeve 48 downwardly so that the conductor ring. will engage the fixed contact element 53,y then the.v circuit for the solenoid of the valve F will be energized, thus opening said Valve as shown (see Figure 6.). A further speedingV up of the shaft 40- willy result` inA the centrifuge members moving the conductor ringv 49 an additional'. distancedownwardly so that it will'` be disengaged fromtthe contact element. 53; and become engaged with the contactA element 54. This will open the circuit of the solenoid of the valve F andY close the circuit of the, solenoid' of the valve R. Valve R Vwill thenbe opened as shown in-Figure 7. Both circuits controlledl by the speed-responsive device may be arranged to be broken,irrespective of the condition et the said speed-responsive device,` by means of a manually-controlledswitchV 60.

The piston P of theservomotorMis so constructed that 'it' willY have associated' with it the electromagnet which' is employedto hold thepis'- ton at the ends-of its .funV stroke.` Tnefpiston' ber- 62 is a coil E4 called the holding coil and en-v closing this coil is another "cylindrical member 65- of =soft .ironl Annular rings 66 `and-6l hold the-coil in position and also further provide support Vmeansfor-k the outer cylindrical member E5.

The piston P is arranged to be carried on-the outer cylindrical member 65 and vto accomplish this there are provided two cylindrical stampings 68 andf69 having flanges. The iianges have received therebetween an annular disk andy all p these elements are riveted together as a unit assembly. Secured to opposite sides ofthis disk are two cupi-shaped packing members 7 I and rI2 arranged in back to back relation.'` The lips of these cups engage the'inner surface of the servocylinder so 'as to provide a' seal-for the piston, preventing air from Vpassing in either direction.

Each packingcup' has associated with it suitable Y means, generally indicated at I3', forpreven'ting any collapse of'a lip of a cup.vv 'l The holding coil M has one end ofV its windings grounded to the piston rod. -The other end of the windings'is varranged to be connected by an insulatedA conductor l'M to the previously referred to conductor :52. The 'conductor 'I4'- extends through a drill passage 'I5 in the' piston rod It. At the Vouter end of thefpassa'ge' 'I5 the conductor is provided-With a Contact member is 'whiehis- :y

insulated from the endV of the'piston rodby nonconducting material 'I'I',;`all as shown'in Figure 5v. Itwill be-noted that the outer'end of the piston rod` I4 is'formed with a lateral extension and this extension is journaled in the lower end of the arm I5 of the lever L; The contact member 'i5 Vis at the end of thisI lateral extension of the piston rod and is arrangedv` to project,I :slightly beyond the end'of said' eXtensionx-The arm I5 carries aconductor finger v'I8 whereby thecontact member'lIS can be' continuously connected tothe' conductor 52. The 'upper end of the nger'is secured to the arm I5 adjacent the pivot I8 ofthe lever L and is'insul'ated from the arm by suitable insulatingmaterial 19.' To the upper end of the vmember 'ISfadjacentjtothe pivot, the conductor 52 `isj. conne'cted. With this arrangement,vit will be seen thatthe conductors 52 and 'I4 are connected together so as to complete'the circuit'to the holding coil and yet pivotal movement between the piston rod I4 and the 4arm I5 isfreely accommodated without any appreciable movement of conductor 52. Asthe arm I5 of the lever L is moved bythe piston rod, the lower 'end of the conductor element13 will merely turn on the contact member 66 and contact will be maintained.

y Since the electro-magnet is to perform a holdingv function, it is 'necessary to provide paramaghetic materialat the ends of the stroke lso as to form` a path for the magnetic lines of forcel created by the electro-magnet.y vThis is accomplished byr providing at the right! end of the 4seryomotor a circular member 80 of soft iron, this member being riveteddir'ectly' to the inside of the right wall II of the motor;Y The' left end wall oi' the-cylinlde'r also has :similarly attached paramagnetic material and,l for purposes which shall later becomefapparent, such being inthe form of twolsoft iron segmental members BI and 82, so

left end of thecylinder.

formed and mounted as toprovide an axial op'em.A

ing. therebetween.

i. It isdesirable that of assuming a central position between the ends of its full stroke whenever the electro-magnetic holding means-is not elfective to hold the piston a-t one end of its stroke, and also when there is no differential fluid pressure acting on the piston.. This centering of. the piston is accomplished by means. of springs acting on opposite.

sides of` the piston. The arrangement of .the

springs is such, however, that each spring is capable of moving the piston only'to the central position and thereafter is no longerf-effective in continuing to apply any force to the pistonA if the piston moves in either direction beyond the central position. Between the piston and the left end wall of the servomotor is` piston after-'the pistonassumes its vcentral posi- Y tion,- said position being shown in Figure Lfthe disk is connected to theV left end wall ofV the cylinder by two collapsible toggles andai. Sinceone link of each toggle `is pivotally connected ,to Vthe left end wall or" the cylinder and the other link is pivotally connected to the diskrnember, the toggles when in extended position.

will limit the movement ofthe disk member'by the spring. Both toggles are so constructed that they will not become fully extendedy when the piston is at the central position.y This is accomplished by providing one of the links of each toggle with a lateral iiange or stop 88 which will overlie-andengage the other linkv adjacent the common lpivot of the toggle. The flanges 88 will -thus prevent the toggles from fullyfextending Vso that these toggles can becollapsed orY folded easily when the piston moves to the In connecting the toggles to the left end wall of the cylinder,v they are arranged to entendi through the opening between the two segmental soft iron members BI and 62 secured as by rivets to the left'end wall of the cylinder. With this arrangement, the toggles, when caused to be folded by movement of the piston in the manner shown in Figure 6, will vthus be received in the opening',

and the holding coil carried by the piston can be brought into engagement with the segmental soft irongmembers. Thesoft viron members in engaging the holding coil extend through the openings in the 'disk member 85. The spring 84 which is to act on the piston and move it from the right end of the cylinder to its central position is preventedfrom acting to move the piston beyond the central position by `means ofV a disk member `39 and iiexible metal straps 'Sii and Si. The inner end of the spring is arranged to act upon the disk member 89 'and through it to move the piston to its central position from the right end of the servomotor. In order to prevent'movement of the disk after'the piston reaches its central position, the flexible straps 96 and SI come into play. One end of each of these straps is connected to the disk member and the other end to the inside of the right end wall of the cylinthe piston P beL capable der; VEach. strap is threaded alternately over and under the convolutions of they spring. Whenv the. spring is compressed, the straps will thus lbeforced. by the Ythreading to become folded in the manner of accordion plaiting. This will prevent the straps from interfering` With the movement of the. piston to the right end of its stroke wherein the soft iron of the electro-magnet. carried by the piston will be broughtv into engagement with thesoft iron member 80r and' thus establish a magnetic holding action.

Operation With the speed-responsive device S substantially at rest and/or the manually-controlled switch 60 open, the condition of all of the elements of theY control system for the servomotor M willv be as shown in Figure l. The piston P will be at the central position of its stroke, having been moved to such position by the centering springs 83 and 84. The reason that these centering springs can move the piston to its central position is that both ends of the servomotor will be connected to atmosphere due to the deenergized condition of the two valves F andR. It will also be noted that they circuit forneither solenoid of the valves will be energized, due to the fact that the conductor ring lllcontrolledv by the speed-responsive device` is not in contact with either fixed contact 53 nor 54 nor is the switch 60 closed. Since the energizing of the holding coil 6.4 of the electromagnet is controlled by the engagement of the conductor ring e9 with either xed contact 53 or '54 while the switch 60 is closed, then of course the holding coil will not be renergized when the speed-responsive device is at rest.

If it is now considered that the manual switch Ellis closed and the rotating element that controls. the speed-responsive device is caused to ro tate, the centrifuge members will be so moved that the conductor ring 49 will be moved downwardly from the position shown in Figure 1 to aA position wherein it will engage the upper fixed Y contact 53. A- circuit will now be closed which will include the solenoid 35 of the-valve F and the`v holding coil.l of the electro-magnet. When the solenoid of valve F is energized it Will open thefvalve and thus connect-the left end of the cylinderl of the servomotor with the tank T. Differential fluid pressurev Will then become efective on the piston P, as the air from the left end of the cylinder of the servomotor is withdrawn. This differential fluid pressure will so act on the piston P as to move it to the lef-t from its central position shown in Figure 1- and to the extreme left end of the cylinder as shown in Figure 6. Since the electro-magnet is now energized, a magnetic path will be established With the fixed segmental. soft iron members 8-land 82 and the electro-magnet Willthus hold the piston at the left end. of the servomotor cylinder IU and maintain the centering spring 83.compressed. As long as the electro-magnet continues to be energized, the piston will remain atthe left end of the cylinder. of the servomotor, even though the diierential` fluid pressure may become linsufcient. to hold the spring 83 compressed. When the pistonmovesto the-left end oi the servomotor from, its central. position, Vthe spring 84: will not follow the. piston as it is, preventedfrom further expanding by the disk 84- and theflexible straps Glland 9|.

If .the speed-responsive device shouldy now. be Yopi-:rated by azgreater speed, the; centrifuge mem;-

berswillbe so moved as to pullthe conductor ring 49f-downwardly and-thus-move it from engage,-l

ment with thefixed contact 53... As soon `asten-- gagement with contact 53. no longerexists,V the solenoid 35 of the-valve F will be de-energized, thus causing this valve Yto ybecome closed and at mosphericr air. toA enter theleft end oftl-ieservo'-Y motor.` Also,V the: holding. coil of thev electromagnet will be de-energized. When thist isdone the. magnetic holdingaction on the.v pistonwill becomeV sol smallv that. the vspring* 83 can.- expandv and move the piston P back` to the,central-posi.

tion.

If the speed ltolwhich. the speed responsivedeviceis responsive should now increase further, theconductor ring 4'9 will be broughtinto engagement with the-contact ,574',` thus closingra.

circuit which willv energize solenoid 35fof..they valve R .and also vcause the coil of the .electro-7 magnet to again be energized. Energization of the solenoid 35y of: the-valve R will openthisv-alve so that the tank- T can-be connected to-the. right end of the servomotor. and-.thus withdrawairfrom. such end.V As a result, a differential fluid4 pressure will be soeffective on. thepiston. that theI piston will be moved to theV extremel right end of. the servomotor, which positionis shown in..Fig ure 7. As the electro-magnet.- is` alreadyzenergized, then as soon asY thefpiston reaches. the. right-end it vW-illr be: held. therev bythe magnetic forces. existing vbetween `the electro-,magnet and.- thesoft iron member xed tothe inside. of the-` right end Wall of thegservomotor.. As the.-piston ismoved to the rightend of thelsenvomotor., the centralizingspring 84-willbe compressed... Theother centralizingf4 spring 83 at the left. end of the. servomotor will not.ho.wever, expand. toactupon the piston, but will..be.hel`d. inLthe; position it hasassumedwhen the .piston was at. the.ce'ntralyp'artr of. its stroke. IIfhis^ isaccomplished. bythe. toggles 8.6 and 8.1... The piston .will remain.. atthe. right end of theservomotor as` long. as. thev speed-- responsive devicev maintains.. the conductonringA 49 engagedwith. the. 'fixed .contact .element 54..

If. the .speedof the member to Whiehthe speedresponsive device is responsive should decrease sothat the conductor ring 49; should become. disengaged. with the Xed'contact element 54;.` the valve R.y will become. closed and the electro-magnet de.-energized Consequently. the' magnetic holding. action .omthepi'stonvvill no longer be so eectiveasto hold'tliepiston .atV the. right Yend of the. servomotor. against.' the' spring. 84 and.. also there will be no differential fluid pressure acting on the pistonas theclosing ofval've' R" connected the, right end ofthe servomotor. to atmosphere. The resultv Will' be that, the centering spring. 8,4' can. expand and movethe'piston back to its central' position as shown in Figure 1.' .If'the conductor. ring` 4.9. 'should'be so movedby the speedresponsive device that it will again engage fixed contact 53'; 'then of course the valve F will. be opened, the electro-magnet energizedV and, the piston moved to theV left" end of the servomotor 'tv-herein it-Will be heldiby vtheacti'orLoflthe el'ec.- tro-magnet', all. in f the..manner previously. de scribed. Y

From the foregoingfdescription. it i's believed'tc oe-apparent thatthe. control means Vfor thenovel ser-vomotor. M is. simple. and; eflicient. to. accomplish. the. results desired. With thez holding coil carried-l by.. thel pistonf.y only. .one holding. coil. is required.. holding` coil. embodied @in theI piston thata. minimum-space-.is used: vThe use of a.v single. holding: coil. carried by. theV piston i also insures that the overall length of the servomotor can be less than where two separate holding coils are `employed with such coils fixed at the ends of the cylinder. The control of the servomotor is also such that centering springs can be employed to vplace the piston at the central portion of its stroke. The electro-magnetic means insures that the piston will be held at the ends of its stroke and insures that the action of the vcentering springs cannot return the piston to its central position if the differential fluid pressure becomes substantially non-existant.

*The-servomotor control means is very useful where vitis desired to control the piston of such motors so that it can assume a held position at either end of its stroke under certain operative conditions, or to assume a central position between the ends of its stroke under other operativeconditions. The use of the speed yresponsive device makes the controlling automatic for predetermined speed conditions of a rotatable member. 'If automatic controlling is not desired, then the speed-responsivedevice can be replacedby manual means, which manual means could also directly `control the `two valves F and R; One particular use of the control means is for servomotors employed in the changing of gear ratios y-of a motor vehicle change-speed gearing.

' Being. aware of the possibility of modifications in .the particular structure shown and described by way of example as embodying the invention, :lit is not intended that the scope of the invention be limited in any manner except in accordance with the appended claims. I claim as my invention:

f1?. In a control means for a-iluid pressure actuated servomotor having a fluid-tight container and a movable element disposedin said container -for movement therein, and a member carried by and movable with said element for actuation in accordance with fluid pressure-responsive movement of said element, a Valve having an open position for establishing differential fluid pres- -sures on opposite sides of said movable element to thereby move said element to a predetermined v position, magnetic means for holding said element in said predetermined position including electromagnetic means carried byand'movable r`with the movable element, fixed paramagnetic and movable therewith for maintainingenergizationro said electromagnetic means whenever said solenoid means is energized despite the adjusted position of said element'. v y `v 2. Ina control means for a fluid pressure actuated servomotor having a casing and a movable element reciprocable in said casing for actuation tto a predetermined position at one end of its stroke by diierential fluid pressure in said casing;

the improvements of an electromagnet carried by and movable with the element, paramagnetic material located in said casing for electromagnetic coaction with said electromagnet when said mov- Aable element is at said one end of its stroke,

meansforenergizing the electromagnet when said element is in its said predetermined position including a conductor substantially coextensive with said element and movable therewith, said electromagnet and said paramagnetic material retaining said element in its said vpredetermined position, and spring means acting on the element to oppose retention of said element at the said one end of its stroke by the magnetic force effective substantially at the saturation point between the energized electromagnet and said paramagnetic material.

3. In controlmeans for a uid pressure actuated servomotor having a piston and a hollow piston'rod, means for establishing diiferent fluid pressure on opposite sides of said piston to thereby move it to a predeterminedy position, and means for holding said piston in said predetermined position including an electromagnetic coil carried by and movable with said piston,-paramagnetic material xed to said fluid servomotor for cooperation with said coil toprovidea magnetic path when said piston is in its said predetermined position, and means for connecting the coil means to a source of electricity including a conductor extending through the hollow piston rod.

4. A fluid pressure actuated servomotor comprising a casing'having spaced end walls and4 a cylindrical inner wall therebetween, a reciprocable actuating rod having an end portion'projecting into `said casing, `an electromagnet including an energizable coil and concentric permeable pole pieces iiXedly mounted on said-rod to surround said end portion thereof, paramagnetic material afxed to one of the end walls of said casing for bridging said pole pieces when said rod end portion is actuated'to vthe corresponding end of said casing,v means carried by said rod for movement therewith to define a fluid-tight Wallv between said electromagnet and said casing inner wall, an electrical conductor eX- tending axially along saidrod and substantially V-coextensive therewith for connection to a source of electrical yenergy to energize said electromagneticfcoil at any adjusted position thereof, and means for introducing iiuid at a pressure different from that of th-e atmosphere into said casing on one side of said wall to effect movement of said rod and said electromagnet toward said one casing wall. l

5. A'iluid pressure actuated servomotor-comprising a casing, a reciprocable hollow rody projecting into said casing, an electromagnet'including an energizable coil mounted on saidrod in surrounding relation thereto, means defining an imperforate wall between the electromagnet and the casing, means including a source of fluid pressure diiferent from atmosphere for establishing differential fluid pressure on opposite sides of said wall'to eiect movement of said rod and said electromagnet relative to said casing, and means for energizing said coil including'an electrical conductor `extending through' said Ying `outwardly fromsaid coil foi-.sealing contact withsaid casing inner walls, andV magnetizable .means secured to one of said end walls for bridging the-gap between said poles when said rod is moved I.to bring said poles into contact therewith.v

. 7..In a fluid pressure actuatedservomotor, a casing, a movable element therein, a Arod l:connected to said element to be actuated thereby,

Yineans for biasing said element away from one end of said casing and to a predetermined .position including a continuously tensioned coil spring'rand astop member for the spring, said .spring being interposed between the end .of said -casing .and said stop member, and said stop mem- -ber being. arranged to apply the lspring force to f said movable element but accommodatingfmovement of-said element relatively thereto in adirectiona'w'ay from the said one end of said .cas-

ing,-.and meansffor-limiting the extent of move- :ment of said stop member by said spring in a direction away from* Ythe said casing Vand: comlprising `a exible member connected tothe said :one .casing end and to said Vstop imember andfbe- .ingthreaded over and under alternate convolutions of said spring.

i8. na fluid pressure actuated servQmoto-r, a casing, a movable element therein, a rod connected to .said element tobe actuated thereby,

`means for biasing said ele-ment in a direction A`favvay from one end of said casing and to a prede- -termined position including a continuous-ly tensioned spring `and .a .stopfmemben said spring; be-

`ing interposed between saidone end of thecasing land said stop member such that the-forcent said spring is applied to said movable element `notwithstanding said element/moves relatively .theretoa-way from the saidone end of the casing, andL-means for limiting the extent of movement .of said stop member :by said springaway from the `said Vone end of'said casing comprisnglinks pivotally V:connected to 4one another and to said one-.casing end and to said stop. :member toffolm iatoggle and :means associated with said links at vtheir-.common vpivot for preventing said ,links from assuming aligned positions.

' 19. In ,a Ycontrol meansfor a vfluid lpressure actuatedpservomotor having a movable element posi- :tionedin a casing provided'with an end wall, said element carrying a reciprocable actuating rod, anzelectromagnetcarried by and movablewith .said .element toward and away from-said end wallfparamagnetic material carried by said end lWall :and projecting into said `casing into the path infirmovement of said element for contact lwith said .,electromagnet when said movable element is lcaused by differential iiuid pressure in said casing to beat one end of its stroke to provide magnetic holding means for the element when the electromagnetis energized, a, stop member .,:slgidably mounted on said actuating rod and in- --terposed between said element -and said paramagnetic material, said member being apertured to accommodate direct electromagnet and para- .'magnetic material contact, a continuously ten- -isioned spring .acting on said slidable member to 1bias said movable element to a position yremote A.from said-paramagnetic material, and collapsible meansfor limiting the movement of said'slida-ble :member'under the iniuence of said spring While accommodating vmovement of said relement -with -respectto said member in a direction .away nfrom said member.

"10.".-In a .controlmeans for .a fluid pressure .actuated vservomotor-movable element positioned 1 in a .casing for reciprocation.ithereinin:response to' Ydiierential vfluid pressures and having an actuating rod, vand means including a :source of iiuid; pressure different Ifrom atmosphere for establishing v.differential fluid pressure ongopposite sides. of said element; fthe improvements `.which comprise an electromagnet carried by and movable with V.said element, paramagnetc Amaterial carried. bysaid casing zadjacentsaid electromagnet when said movable `element is moved by dif- Aferent'ia-l fluid-pressures Atoene end of its vstroke extension :and said: .paramagnetic 'material being :positioned with respect to saidtoggle so thatithe toggle, .when collapsed lby the movement of .said movableel-ement of the servomotor, ,willbe disposed rearwardly of a fforward'face of Ysaid para- Ymagnetic material.

1l. Ina `control means Yfor a Ldoubleacting fluidpressure actuated servomotor'gh'avinga movable element, a source of fiuid pressure different from atmosphere, valve means -for controlling the communication' between said-source ,and opposite ends .oflsaidservomoton lthe, improvements of Yelectromagne'tic means forholding said element-,ateach'end of the servomotor .and-including energzable'coil telescopicallyl mount- .ed on and V.secured to saidmovable element :for

I moyementtherewitn, meansffor seleotivelyyoontrolling said ,valve .mea-ns softhat csaid servomotor element `canbe moved byfuidpressure to either end of said,servomoton electrical v-,circuit means Yfor energizing saidv coil, .and means `for v closing said elec-tricalmeans to Vthereby energize I' the -coil only when said element is'caused tobe 'moved to fan end of said motoribya controlling of fsaidvalve means. f

12. In a control means lfor a double acting --fluid pressure vactuated servomotor having an axially movable piston, a source of -uid pressure Vdifferent from atmosphere, valve means for controlling the communication between said source 'andopposite ends of said -servomotor; the improvements of electromagnetic means for holding said .element at each end ofthe servomotor, including van -energizable coil concentric with and telescopically received by said piston to fit substantially within-the normal axial dimensions of said piston, said coil beingmovable with said piston; and fixed -paramagnetic materialcarried by each end of said servomotor, and electrical means including circuits and switches vfor selectively controlling said valve means so that said servomotor element can be moved by duid pressure to either end of said-servomotor and for Yadditionally causing energization of said coil so that said elementv will be held in its end'position lby said electromagnetic ineans.

13. In a control means-for a double acting :duid pressure actuated servomotor having an axially movable element, a source of fluid pressure'different `from atmosphere, `valve lmeansA forV controlling the communication between said source and opposite ends of said servomotor, electromagnetic means for holding said element at each end of said servomotor and comprising an e er-, gizable coil mounted on said movable element and lying substantially within the movable element, said coil being movable axially with said element, electrical means including switches for selectively controlling said valve means so that said servomotor element and said coil can be moved by iluid pressure to either end of said servomotor, and.V means for energizing said coil so that said element will be held in its end position by said electromagnetic means.

14. In control means for a double-acting fluid pressure energizable servomotor having a movable piston controllable in response to the speed of a rotating member; a source of iluid pressure different from atmosphere for energizing the servomotor; valve means for selectively controlling application of said fluid pressure to opposite ends of the servomotor to energize the same; electromagnetic means for holding said piston at either extreme end of the servomotor, including an energizable coil carried by said piston for movement therewith and confined substantially within the axial dimensions of said piston; electrical means including at least a pair of switches for controlling said valve means; and a speedresponsive device driven from said rotating member for controlling said switches to cause energization of the servomotor by application of said fluid pressure to a selected end thereof to effect movement of said piston to said extreme end, and for simultaneously energizing said coil to retain said piston in said extreme end by said electromagnetic means.

GLENN T. RANDOL.

REFERENCES CITED The following references are of record in the le of this patent:

l UNITED STATES PATENTS 

